Least was used to boost octake and also lubricated valves.
Can you link documentation to support your post?
10 seconds on Wikipedia:
In motor fuel[edit]
TEL was extensively used as a gasoline additive beginning in the 1920s,[10] wherein it served as an effective antiknock agent and prevented exhaust valve and valve seat wear. Concerns were raised in reputable journals almost immediately of likely health outcomes of fine particles of lead in the atmosphere.[11]
Valve wear preventive[edit]
Tetraethyl lead works as a buffer against microwelds forming between the hot exhaust valves and their seats.[12] Once these valves reopen, the microwelds pull apart and leave the valves with a rough surface that would abrade the seats, leading to valve recession. When lead began to be phased out of motor fuel, the automotive industry began specifying hardened valve seats and upgraded exhaust valve materials to prevent valve recession without lead.[13]
Antiknock agent[edit]
A gasoline-fueled reciprocating engine requires fuel of sufficient octane rating to prevent uncontrolled combustion known as engine knocking (knock or ping).[9] Antiknock agents allow the use of higher compression ratios for greater efficiency[14] and peak power.[15] Adding varying amounts of additives like low percentage TEL or high percentage ethanol to gasoline, allowed easy, inexpensive control of octane ratings. TEL offered the business advantage of being commercially profitable because it could be patented.[10] Aviation spirits with TEL used in WWII reached 150 octane to enable supercharged engines such as the Rolls-Royce Merlin and Griffon to reach high horse power ratings at altitude.[16] In military aviation, TEL manipulation allowed a range of different fuels to be tailored for particular flight conditions.
In 1935 the licence to produce TEL was given to I.G.Farben enabling the newly formed German Luftwaffe to use high-octane gasoline. A company, Ethyl GmbH, was formed that produced TEL at two sites in Germany with a government contract from 10 June 1936.[17]
“Least was used to boost octake”
I think you meant to say “yeast was used to boost oatcakes”.